Portman, R-Ohio, announced his change of heart on the issue last week, saying he supports gay marriage because his son is gay. Portman said he does not want the Supreme Court to overturn the Defense of Marriage Act, but instead believes Congress should repeal part of the law and that states should work legislatively to permit gay marriage.

"It's his decision," Priebus said at a National Press Club event this morning. "It's not a matter of whether I support his decision. I support him doing what he wants to do as an elected person and as an American. If that's is opinion, I support him having that opinion."

Priebus also said he did not believe Portman's decision to support gay marriage would have an impact on financial support from his party. "He will be supported," he said.

Priebus spoke at the press club to unveil the GOP's long-awaited "autopsy report" investigating why it lost during the 2012 elections. Among the RNC's suggested fixes: making the presidential primary process shorter, enacting comprehensive immigration reform and improving the party's voter database and digital technology.